Medical devices that can benefit from the present invention include those that are introduced endoluminally and are used to deploy expandable embolic particles for the purpose of occluding a location of concern within a patient, such as an aneurysm.
An aneurysm is an abnormal bulge or ballooning of the wall of a blood vessel, which most commonly occurs in arterial blood vessels. Aneurysms typically form at a weakened point of a wall of a blood vessel. The force of the blood pressure against the weakened wall causes the wall to abnormally bulge or balloon outwardly. Aneurysms, particularly intracranial or neovascular aneurysms, are a serious medical condition because an aneurysm can apply undesired pressure to areas within the brain. Additionally, there is the possibility that the aneurysm may rupture or burst leading to serious medical complications including mortality.
When a patient is diagnosed with an unruptured aneurysm, the aneurysm is treated in an attempt to prevent the aneurysm from rupturing. Unruptured aneurysms have traditionally been treated by what is known as “clipping.” Clipping requires an invasive surgical procedure wherein the surgeon makes incisions into the patient's body to access the afflicted blood vessel. Once the surgeon has accessed the aneurysm, he or she places a clip around the neck of the aneurysm to block the flow of blood into the aneurysm which prevents the aneurysm from rupturing. While clipping may be an acceptable treatment for some aneurysms, there is a considerable amount of risk involved with employing the clipping procedure to treat intracranial aneurysms because such procedures require open brain surgery.
More recently, intravascular catheter techniques have been used to treat intracranial aneurysms because such techniques do not require cranial or skull incisions, i.e., these techniques do not require open brain surgery. Typically, these techniques involve using a catheter to deliver embolic devices to a preselected location within the vasculature. For example, in the case of an intracranial or neovascular aneurysm, methods and procedure, which are well known in the art, are used for inserting the distal end of a delivery catheter into the vasculature of a patient and guiding the catheter through the vasculature to the site of the intracranial aneurysm. A vascular occlusion device is then attached to the end of a pusher member which pushes the occlusion device through the catheter and out of the distal end of the catheter where the occlusion device is delivered into the aneurysm.
Once the occlusion device has been deployed within the aneurysm, the blood clots on the occlusion device and forms a thrombus. The thrombus forms an occlusion which seals off the aneurysm, preventing further ballooning or rupture. The deployment procedure is repeated until the desired number of occlusion devices are deployed within the aneurysm. Typically, it is desired to deploy enough coils to obtain a packing density of about 20% or more, preferably about 35% and more if possible.
The most common vascular occlusion device is an embolic coil. Embolic coils are typically constructed from a metal wire which has been twisted into a helical shape. One of the drawbacks of embolic coils is that they do not provide a large surface area for the blood to clot. Additionally, the embolic coil may be situated in such a way that there are relatively considerable gaps between adjacent coils in which blood may freely flow. The addition of extra coils into the aneurysm does not always solve this problem because deploying too many coils into the aneurysm has the potential to lead to an undesired rupture.
Another endoluminal approach for treating an aneurysm is to use a delivery catheter to deliver expandable embolic particles into the aneurysm. Upon deployment, the embolic particles expand to fill in the aneurysm and block off blood flow into the aneurysm. Typically, the embolic particles in the expanded state have a larger cross-sectional extent than that of the delivery catheter. The embolic particles are compressed to fit within the delivery catheter, and the delivery catheter constrains the embolic particles, keeping the embolic particles in the compressed state as the embolic particles travel through the delivery catheter. The friction created by the compressed embolic particles contacting the inner wall of the delivery catheter makes it very difficult, if not impossible, to move the embolic particles through the delivery catheter with the use of a pusher element. Typically the movement of such embolic particles is effected by hydraulic forces, i.e., applying fluid pressure to the embolic particles to move them through and out of the delivery catheter.
The use of hydraulic pressure to move embolic particles creates at least two problems. First, after the first embolic particle has been extruded from the distal end of the catheter, the pressure required to extrude the second embolic particle is lessened, and the pressure required to extrude the third embolic particle is less than the pressure to extrude the second embolic particle and so on. Therefore, under prior approaches, the velocity of each embolic particle extruded becomes faster and faster as delivery proceeds. This can create a dangerous situation wherein the later extruded embolic particles exit the delivery catheter at undesirably high velocities. Traveling at such undesired higher velocities, the extruded embolic particles have the potential to cause damage when contacting the already weakened wall of the vessel.
Another problem with the use of hydraulic pressure is “jetting.” “Jetting” refers to the force and speed at which the fluid exits the distal end of the delivery catheter, as well as the volume of fluid that exits the delivery catheter. A small amount of jetting occurs as both the embolic particles and fluid exit the delivery catheter; however, the jetting that occurs after the last embolic particle has exited the distal end of the catheter is of concern because as the last embolic particle exits the delivery catheter there is a release of a large amount of pressure from the catheter into the location of deployment. This release pressure results in a relatively large volume of fluid rapidly entering the deployment site with an undesired force being applied to the already damaged walls of the vessel. In the case of an aneurysm, a large jetting force has a potential catastrophic consequence of rupturing the aneurysm.
Therefore, there remains a need that is recognized and addressed according to the present invention for embolic particle delivery systems and methods for delivering embolic particles in order to allow control of the velocity of the embolic particles, and decreases or limits the effects from jetting and decreases the volume of fluid that is introduced from the catheter into the deployment site.